The present invention relates to a stapler for driving staples into an object, such as a sheaf of papers, said stapler comprising a base, in which a cassette is removably inserted, said cassette containing wire-shaped staple blanks, which are juxtaposed and releasably interconnected to form a strip of staple blanks, the strip being partially exposed through an opening in the cassette, a reciprocable staple shaper, which is arranged to successively shape staple blanks from the strip into U-shaped staples, a reciprocable staple driver, which is arranged to successively drive the staples formed into an object, and an advancing mechanism, which is arranged to advance the strip step by step in the direction of the staple shaper and the staple driver and which, to this end, is movable back and forth in the advancing direction of the strip, said direction coinciding with the direction in which the cassette is removed from the base, and in the opposite direction thereof and which comprises a feeding plate, which engages one flat side of the strip through said opening in the cassette so as to slide across this flat side when the advancing mechanism is being moved in the direction opposite to the advancing direction and to advance the strip when the advancing mechanism is being moved in the advancing direction.
A prior-art cassette of the type described above is described in more detail in EP 0 636 058. This cassette includes the staple shaper and the staple driver. Thus, when the cassette is removed from the base of the stapler, these elements are also removed. In a stapler according to prior art, in which cassettes including staple shaper and staple driver are used, the cassette is inserted into the base of the stapler from the front, i.e. the direction of insertion is the opposite of the advancing direction of the strip of staple blanks in the stapler. In this case, the cassette is inserted by means of guide ribs on the base and guide lugs on the cassette along a linear path of insertion, which is located in such manner relative to the mechanism arranged to advance the staple blanks in the cassette that the insertion takes place without the staple blanks touching the feeding plate of the advancing mechanism. Each of the guide ribs has in its portion located at the very back of the base a recess, into which a corresponding guide lug on the cassette can be inserted. When the cassette has reached its position inserted in the base, these recesses allow it to be moved a short distance perpendicularly to the direction of insertion so as to be moved in the direction of the advancing mechanism so that the strip of staple blanks is caused to engage the feeding plate. The feeding plate is forwardly inclined at an angle, i.e. in the direction opposite to the direction of insertion of the cassette, thus making it necessary to insert the cassette in such a position that the strip of staple blanks will not come into contact with the feeding plate during the insertion of the cassette. The removal of the cassette from the base is less critical in this respect. However, when removing the cassette, the cassette must, before it can be pulled out, first be inclined or tilted in such manner that the guide lugs inserted into the recesses are removed from the recesses in the guide ribs. When the cassette is inclined in this way, there is a considerable risk, if the cassette is carelessly handled and for some reason removed before it is empty, of the staple blanks in the cassette coming into contact with the bending die, over which the staple blanks are bent during operation of the stapler, and thus being damaged. Because the passage in the base into which the cassette is inserted must be sufficiently large to allow the cassette to be inclined in this way, there is also a considerable risk of the cassette being held in a slightly inclined position while being inserted into the base. Again, the staple blanks risk coming into contact with the bending die, which may damage them.
The object of the present invention is therefore to provide a stapler, in which the above-related problems are eliminated or at least significantly reduced.
According to the invention, this object is achieved with a stapler, which is of the kind stated by way of introduction and characterized in that the advancing mechanism comprises means, which are arranged to interact with the cassette, which has been removably inserted into the base, so as to move the feeding plate, during an initial phase of the cassette""s removal from the base, to a neutral position, in which it has been disengaged from the strip, and to move the feeding plate, during a final phase of the reinsertion of the cassette or the insertion of a similar cassette into the base, to an engagement position, in which it engages the strip of the cassette, that said means comprise a slide, which is movable back and forth in the advancing direction and the opposite direction thereof between a rear position and a first front position, the slide being spring-biased in the advancing direction so as to be moved, when the cassette is being removed from the base, to a second front position located a short distance ahead of the first front position, said means being arranged in such manner that the feeding plate is in its engagement position during the slide""s movement back and forth between the rear position and the first front position, and that it is in its neutral position when the slide is in the second front position, the slide, in the second front position, protruding such a distance from the base that it is hit, in the final phase of the insertion of a cassette, by the cassette and pressed to the first front position.
In a preferred embodiment, the feeding plate is pivotally mounted on the slide about an axis perpendicular to the advancing direction, the feeding plate being pivotable between its engagement position and its neutral position, and said feeding plate being spring-biased towards its engagement position.
Said means preferably comprise a ramp means, which is fixedly arranged in the base and located in such manner that the feeding plate, during the movement of the slide from the first front position to the second front position, hits the ramp means and is pivoted thereby from its engagement position to its neutral position.